Alkyldichlorobenzoic acids



United States Patent "cc 3,282,991 ALKYLDICI-ILOROBENZOIC ACIDS David X.Klein, Montclair, and Theodore A. Girard, Wayne Township, PassaicCounty, N.J., assignors to Tenneco Chemicals, Inc., formerly HeydenNewport Chemical Corporation, New York, N.Y., a corporation of DelawareNo Drawing. Filed Oct. 29, 1963, Ser. No. 319,703

12 Claims. (Cl. 260-501) This application is a continuation-in-part ofour copending application Serial No. 714,030, now abandoned, filedFebruary 10, 1958, and our copending application Serial No. 203,485,filed June 19, 1962, now Patent No. 3,236,623 which is acontinuation-in-part of said application Serial No. 714,030.

The present invention relates to novel compounds and the production ofsuch compounds.

In accordance with this invention it has been discovered that certainmonoalkyldichlorobenzoic acids have unusual and valuable activity asherbicides and particularly as selective herbicides. These compounds maybe applied to soil or other medium normally supporting plant growth orto existing plants to inhibit or control the growth of plants. They maybe applied to an area containing a crop to prevent the growth of weedstherein, or they may be applied to an area to keep it free from allplant growth.

The herbicidal monoalkyldichlorobenzoic acids have the formula in whichone of the symbols R and R is a chlorine atom and the other is an alkylgroup containing from 1 to 4 carbon atoms. These compounds include, forexample, 2-methyl-3,G-dichlorobenzoic acid, 2-propyl-3,6-dichlorobenzoicacid, 2-butyl-3,6-dichlorobenzoic acid, 2,3-dichloro-6-methylbenzoicacid, and 2,3-dichloro-6-butylbenzoic acid. Esters, salts, and amides ofthese acids also have herbicidal activity.

The herbicidal monoalkyldichlorobenzoic acids may be applied as such toplants or to the soil, or they may be applied in the form of compoundsthat under the conditions of use yield the acids. Thus, they may beapplied as salts, esters, or amides that will yield the acids on contactwith soil or plant moisture as is well known in the art with regard toorganic acid herbicides. Accordingly, hydrolyzable salts, esters, andamides are obvious equivalents of the acids.

While any of the metal, ammonium, and amine salts of the acids may beused as herbicides, the most effective are the alkali metal and alkalineearth metal salts, for example, the sodium, potassium, lithium, calcium,and barium salts; the ammonium salt; and the monoand dialkylamine andalkanolamine salts in which the alkyl and alkanol groups contain from 1to 4 carbon atoms, for example, the dimethylamine, monobutylamine,diethanolamine, monomethanolamine, and dibutanolamine salts. Theherbicides may also be used in the form of esters. Alcohols that may bereacted with the acids to form herbicidal esters include alkanolscontaining from 1 to 6 carbon atoms, monohydric ether alcohols, andalkylene glycols containing from 2 to 6 carbon atoms. Illustrative ofthese alcohols are methanol, ethanol, propanol, butanol, hexanols,ethylene glycol, propylene glycol, diethylene glycol, triethyleneglycol, ethylene glycol monomethyl ether, ethylene glycol monobutylether, and diethylene glycol monoethyl ether. Amides of the acids, forexam- Patented Nov. 1, 1966 ple, 2,3,6-monoalkyldichlorobenzamides,N,N-dimethyl- 2,3,6 monoaLkyldichlorobenzamides, N,N diisopropyl-2,3,6-monoalkyldichlorobenzamides, and N-n-butyl-2,3,6-monoalkyldichlorobenzamides, may be used. These derivatives may beprepared by methods that are well known to those skilled in the art.

While the herbicidally-active products may be applied as such for thecontrol of weeds and in the sterilization of soil with regard to plantgrowth, they are ordinarily and preferably used in combination with aninert diluent or carrier to make it easier to measure accurately and toapply evenly the small amounts of the herbicides that are required tocontrol plant growth as well as to apply them in the form that will bereadily dispersed through the soil and/or absorbed by the plants. Thosecompounds that are sufficiently soluble in water, such as the alkalimetal and ammonium salts, can be formulated into sprayable compositionsby dissolving them in Water. Alternatively,

the compounds may be mixed with or deposited upon an.

inert finely-divided solid carrier, such as natural clays, diatomaceousearth, silica, walnut shell flour, and the like, and employed as dusts.Such mixtures may also be dispersed in water with or without the aid ofa wetting agent and the resulting aqueous dispersions employed assprays. Herbicidal granules or pellets are often used when theapplication is primarily to the soil. Pellets may be made by extrudingmoistened, powdered mixtures of the herbicide and a powdered inertdiluent under high pressure through dies. Granules may be prepared byimpregnating granular carriers, such as granular clays, or bygranulating mixtures of the herbicide and a powdered inert diluent. Theherbicidal compounds may also be used as the active constituents inketone, ether, alcohol, or hydrocarbon solutions or in oil-in-wateremulsions.

The concentration of the herbicidal compound in the composition may varywidely and depends upon a number of factors, the most important of whichare the amount of composition to be applied per unit of area and thetype or types of plants being treated. In most cases the herbicidalcompounds are applied in the form of sprays, dusts, or granules thatcontain from approximately 0.1% to by weight of the active component.Two or more of the herbicidal compounds of the present invention may bepresent in the compositions; if desired, other herbicidal compounds mayalso be present.

The monoalkyldichlorobenzoic acids of the present invention may beprepared by any convenient process. For example,2,3-dichloro-G-methylbenzoic acid and 2-methyl- 3,6-dichlorobenzoic acidmay be prepared by a process which involves the nuclear dichlorinationof o-xylene, the side-chain chlorination of the dichloro-o-xylene toform methyldichlorobenzyl chloride, and the reaction of themethyldichlorobenzyl chloride with an alkali metal salt of a saturatedmonocarboxylic acid to form a methyldichlorobenzyl ester which is thenoxidized to methyldichlorobenzoic acid. The product of this process is amixture containing at least 60% of methyldichlorobenzoic acid and smallamounts of methylmonochlorobenzoic acid, methyltrichlorobenzoic acid,and methyltetrachlorobenzoic acid. The methyldichlorobenzoic acids maybe separated from the other products of the reaction, for example, byfractional distillation, or the mixture of methylchlorobenzoic acids maybe used in the herbicidal compositions.

The methyldichlorobenzoic acid fraction resulting from theaforementioned procedure is a mixture of isomers containingapproximately 50% to of isomers having a chlorine atom in the 3-positionand a methyl group and a chlorine atom in the 2- and 6-positions of thearomatic nucleus, that is, 2-methyl-3,6-dichlorobenzoic acid and2,3-dichloro-6-methylbenzoic acid. Smaller amounts of the other isomers,for example, 2-methyl-3,4-dichlorobenzoic acid,2-methyl-4,S-dichlorobenzoic acid, and 2- methyl-5,6-dichlorobenzoicacid, may also be present. The relative amounts of2-methyl-3,6-dichlorobenzoic acid and 2,3-dichloro-6-methylbenzoic acidthat are present in the mixture of methyldichlorobenzoic acid isomersmay vary widely. In most cases approximately 0.1 part to 10 parts byweight of 2,3-dichloro-6-methylbenzoic acid are present for each part byweight of 2-methyl-3,6-dichlorobenzoic acid.

The present invention is further illustrated by the examples thatfollow. It is to be understood, however, that these examples are not tobe construed as being limitative, but are furnished merely for purposesof illustration.

Example 1 A mixture of isomeric methyldichlorobenzoic acids containing2,3-dichloro-6-methylbenzoic acid and Z-methyl- 3,6-dichlorobenzoic acidwas prepared by the following procedure:

Gaseous chlorine was bubbled through a mixture of 500 g. of o-xylene and5 g. of iron filings at 15 to C. for 5 hours. At the end of this timethe weight of the mixture had increased by 323 g. The chlorinatedo-xylene mixture was washed with five 1000 ml. portions of water andthen distilled under reduced pressure. The dichloro-o-xylene fraction,which boiled at 104-108 C./ 12-14 mm., weighed 331.3 grams and contained40.11% Cl (calculated for dichloroxylene, 40.6% C1).

Two hundred grams of this dichloro-o-xylene was chlorinated at 205 210C. for three hours. At the end of this time the weight of the reactionmixture had been increased by 39 grams, the calculated weight incresefor the addition of one gram atom of chlorine per gram molecular weightof dichloro-o-xylene.

The methyldichlorobenzyl chloride resulting from the above-describedside-chain chlorination was heated with 118.3 grams of sodium formateand 600 ml. of acetic acid at reflux temperature for 8 hours. Followingremoval of the acetic acid by distillation under reduced pressure andwashing of the product with 500 ml. of water, 215.4 g. of crudemethyldichlorobenzyl formate was obtained. Oxidation to thecorresponding acid was accomplished by heating 105 g. of the ester with617.5 g. of 70% nitric acid at reflux temperature for three hours. Theoxidation product was cooled, poured into .1000 ml. of water, and thenextracted with three 300 ml. portions of benzene. The combined benzeneextracts were extracted with 410 g. of a 5% sodium hydroxide solution.After the addition of ml. of 36% hydrochloric acid, the sodium hydroxideextract was treated with 3 g. of activated carbon and filtered. Thefiltrate was acidified with 100 g. of 36% hydrochloric acid, and theprecipitated product was isolated by filtration and dried at 55 60 C.Approximately 58 g. was obtained of a product which was a mixture ofisomeric methyldichlorobenzoic acids containing major amounts of the2,3-dichloro-6-methyl isomer and the 2-methyl-3,6-dichloro isomer andminor amounts of the 2-methyl-3,4-dichloro isomer and the 2-methyl-4,5-dichloroisomer.

Example 2 Seventy-five grams of a mixture of isomericmethyldichlorobenzoic acids prepared by the procedure described inExample 1 was heated at its reflux temperature for 8 hours with 750 ml.of methanol and ml. of concentrated sulfuric acid. Following the removalof unreacted methanol by distillation under reduced pressure, theresidue was dissolved in benzene. This solution was washed with waterand was then extracted with 320 ml. of a 5% sodium hydroxide solution.The alkaline extract was treated with activated carbon at 50 C.,filtered, cooled to 20 C., and acidified with 36% hydrochloric acid. Theprecipitated acid was isolated by filtration and then recrystallizedtwice from cyclohexane, twice from ligroin, and then from nitroethane.The purified 2,3-dichloro-6- a (complete kill).

methylbenzoic acid resulting from this procedure had a melting point of9192 C. and an acid number of 274 (calculated for C H O Cl Acid No.274).

The benzene solution of methyl esters of methyldichlorobenzoic acidisomers not having a chlorine atom ortho to the carboxy groups of theacid and from which the methyldichlorobenzoic acids, each having achlorine atom ortho to the carboxyl group, had been extracted wasevaporated to dryness. The residue was heated with 11.8 g. of sodiumhydroxide, 23.6 g. of water, and 200 ml. of ethanol at refluxtemperature for 8 hours. Following the .removal of ethanol and water bydistillation under reduced pressure, the residue was dissolved in waterand the resulting solution was clarified by filtration, acidified to pH1, and again filtered. After being dried at 55-60 C., the product, whichcontained 2-methyl-3,4-dich1orobenzoic acid and2-methyl-4,5-dichlorobenzoic acid, was purified by recrystallizationfrom benzene. The components of this mixture were then separated fromfractional distillation.

Example 3 In this series of tests, groups of flats containing soil wereplanted with rape, lambs quarters, alfalfa, vetch, and timothy seeds,respectively. Each flat contained seeds of one kind and was treated withone herbicide at one dosage. The herbicide was applied in the form of adilute aqueous solution of sodium 2,3-dichloro-6-methylbenzoate. Theamount of solution used was such as to apply the amount of the sodiumsalt equivalent to the amount of 2,3-dichl0ro-6-methylbenzoic acid setforth under Dosage in Table I. For comparative purposes flats in eachgroup Were treated with aqueous solutions containing the sodium salt of2,4-D. (2,4-dichlorophenoxyacetic acid). In each case the herbicidewasapplied to the soil in the. fl-ats on the same day that the seeds wereplanted. The results of the tests, which were observed ten days afterplanting, are given in Table I.

In tables I and II the letters D, S, and I refer to density of theplants, size of the plants, and injury to the plants, respectively. Theeffectiveness of the herbicides, as determined by comparison withuntreated planings, is indicated in the tables by the numbers 0 through100 in increasing order of effectiveness. Thus 0 indicates no herbicidalactivity and 100 maximum activity TABLE I.AC'IIVITY OF 2,3-DICHLORO-6-MEZOIO ACID AS A PRE-EMERGENCE HERBIC I DE 2,3-dichl0r0-6- 2,4-D Dosage,methylbenzoie acid Plant Species Lbs. [Acre D S I D S I Rape 0. 25 20 6040 0 20 20 O. 5 40 60 40 20 60 20 1. 0 60 6O 60 60 2O 2. 0 80 100 80 8080 Lambsquarters 0. 2' 0 40 20 0 0 20 0. 5 20 60 4O 0 0 20 1. O 20 60 600 40 20 2. 0 60 60 60 40 40 40 Alfalfa 0. 25 0 40 20 0 20 20 0. 5 20 806O 20 60 40 1. 0 60 80 80 40 80 80 2. O 60 80 80 60 80 80 Vetch 0. 25 2040 60 0 0 20 0. 5 40 60 60 20 20 40 1. 0 60 60 80 40 40 60 2. 0 80 60 8060 60 6O Timothy 0. 25 20 60 40 0 20 0 0. 5 40 60 40 20 40 20 1. 0 40 606O 40 40 20 2. 0 80 80 80 60 60 60 From the' data in Table I it can beseen that 2,3-dichloro-6-methylbenzoic acid is more eflective as aherbicide than is 2,4-D when applied before the emergence. of bothdicotyledonous plants (rape, lambs-quarters,

alfalfa, and vetch) and monocotyledonous plants (timy Example 4 Groupsof flats containing soil were planted with rape,

6 Example 5 A series of experiments was carried out in which thepost-emergence herbicidal activity of the product of Example 1 wascompared to that of certain other methyldilambsquarter, millet, andtimothy seeds, respectively. 5 chlorobenzoic acid isomers. In thesetests a group of flats Each fiat contained seeds of one kind and wastreated containing rape seedlings was sprayed with aqueous soluwith oneherbicide at one dosage. The herbicides were tions of the sodium saltsof the acids at dosages ranging applied in the form of dilute aqueoussolutions of their from 0.5 pound to 16 pounds per acre, these dosagessodium salts with the quantity of solution used being such indicatingthe equivalent amount of acid applied as the as to apply the amount ofsalt equivalent to the amount salt. The results of the tests wereobserved 43 days after of acid indicated in the Dosage column. Thesolutions were appliedto the soil in the flats on the day the seedsapplication of the test materials. The effects observed at this time aresummarized in Table III.

TABLE III.-ACTIVITY OF METHYLDICHLOROBENZOIC ACIDS AS POST-EMERGENCEHERBICIDES Product of Example 1 3, 5-dich1oro-4-methylben- 4,6-dichloro-2-methylbenzoic Acid zoic Acid Dosage, LbJAcre PercentPercent Percent Plants S 1 G 2 L 3 Plants S G 2 L 3 Plants S G 2 L 3Killed Killed Killed 0 0 0 0 0 0 0 0 0 0 10 0 4O 40 0 0 0 0 0 O 0 0 4080 0 0 0 0 0 0 0 0 95 60 100 80 O 0 0 0 0 20 0 0 100 0. 0 0 0 [l 20 0 0100 0 0 0 0 0 4O 0 0 1 S degree of reduction of size. 2 G degree ofgalling.

were planted. The results, which were observed the stated number of daysafter planting, are summarized in Table II.

3 L degree of attenuation (narrowing and folding of secondary leaves).

From the data in Table III it will be seen that the product of Example 1killed all of the plants at 8 and 16 pounds per acre and substantialnumbers of plants at 2 TABLE II.-ACTIVITY OF METHYLDICHLOROBENZOIO ACIDSAND MIXTURES OF METHYLDICHLOROBENZOIC ACIDS AS PRE-EMERGENCE HERBICIDESMixture of 2methyl-3A-dl- Product of Example 12,3d1chl0r0-6-methylbenzoic 2 methyl-4,t'rdichloroben chlorobenzoic acidand 2- Dosage, acid zoic acid methy1 4, S-dichloroben- Plant SpeciesLbs/Acre zoie acid Days D S I Days D S I Days D S I Days D S I Rape 1. 019 60 80 80 24 60 80 60 r Lambsquarters l. 0 19 60 60 40 27 20 40 20Timothy 1. 0 7 40 40 4O 24 80 2.0 7 8O 80 60 24 100 Millet 1. O 19 0 4020 24 40 2. 0 l9 0 40 20 24 20 The data in Table II indicate that theherbicidal activity of the product of Example 1, which is a mixture ofisomeric methyldichlorobenzoic acids including the 2,3-dichloro-6-methyl isomer and the 2-methyl-3,6 -dichloro isomer isapproximately equivalent to that of purified 2,3-dichloro-6-methylbenzoic acid. Inasmuch as the Z-methyl-4,5-dichloroisomer and the mixture of this isomer with the 2-methyl-3,4-dichloroisomer have little herbicidal activity, the mixture of isomeric acidsincluding 2,3-dichloro-6-methylbenzoic acid and2-methyl-3,6-dichlorobenzoic acid shows a synergistic herbicidal efiectin that its activity is greater than the sum of the activities of theindividual acids based on the amounts of each present in the mixture.

Example 6 A series of experiments was carried out in which a mixture ofmethylchlorobenzoic acids was evaluated as a herbicide against a widevariety of crop plants and weeds. The methylchlorobenzoic acid mixtureemployed contained 0.3% of methylmonochlorobenzoic acid, 70.0% ofmethyldichlorobenzoic acids, 24.5% of methyltrichlorobenzoic acids, and5.2% of methyltetrachlorobenzoic acids. The methyldichlorobenzoic acidfraction contained approximately 75% of 2-methyl-3,o-dichlorobenzoicacid and 2,3-dichloro-6-methylbenzoic acid and small amounts of2-methyl-3,S-dichlorobenzoic acid, 2-methyl-3,4-dichlorobenzoic acid,2-methyl-4,5-dichlorobenzoic acid, and 4- methyl-2,5-dichlorobenzoicacid.

In these tests the herbicidal mixture was applied as an aqueous solutioncontaining an amount of the dimethylamine salts of the acids equivalentto approximately two pounds of the acids per gallon. The amount ofsolution used was such as to apply the amount of salt equivalent to theamount of acid indicated in the Dosage column. The results of thesetests are given in Table IV.

TABLE IV.HERBICIDAL ACTIVITY OF MIXTURE OF METHYLCHLOROBENZOIO ACIDSCONTAINING 2,3-DI- CHLORO-6-METHYLBENZOIC ACID AND 2METHYL-3,6-DICHLOROBENZOIC ACID As Pre-Emergence As Post-Emergence HerbicideHerbicide Plant Species Dosage Dosage 2 Lbs./ 4 Lbs./ 2 Lbs./ 4 Lbs./Acre Acre Acre Acre 100 100 95 100 90 100 100 100 80 95 90 95 80 100 7090 80 90 100 100 70 90 70 90 100 100 100 100 90 100 100 100 100 100 100100 70 90 95 95 20 Lespedeza 100 100 95 100 Lima Beans. 95 95 90 95 Oats20 50 30 50 Peanuts 90 100 100 100 Peas a .50 90 100 100 Red Clover 100100 100 100 Safiiower--. 100 100 95 100 Snapbeans 95 100 95 95 Sorghum-80 90 50 7O Soybeans 100 100 100 100 90 95 90 95 80 90 50 70 100 100 9595 100 100 95 100 90 95 10 30 0 10 Other Grasses 9O 95 2O 40Lambsquarters 100 100 90 95 Mustard 90 100 95 i 95 Pigweed 100 100 90 95Example 7 o-Toluic acid in sulfuric acid was ring chlorinated withgaseous chlorine in the presence of iodine as a catalyst.

The product was a mixture of chlorinated methylbenzoic acids andcontained 45% of monochlorinated acid, 45% of dichlorinated acid, and10% of trichlorinated acid. The mixture was partially reacted with anexcess of 2- ethylhexanol at 200 C. The non-esterified acid was reactedwith sodium hydroxide and the water soluble sodium salts were separatedfrom the esters. The salts were then converted back :to the acids byreaction with hydrochloric acid. The esters (Fraction A) were the estersof those chlorinated acids not having a chlorine atom in a poistionortho to, the carboxyl group. The unesterified acids (Friction B) werethe acids having the methyl group in one position and a chlorine atom inthe other position ortho to the carboxyl group.

Fraction A contained 62% of monochloro-methylbenzoic acid ester, 36.5%of dichloro-methylbenzoic acid ester, and 1.5% oftrichloro-methylbenzoic acid ester. This fraction was distilled and adichloro-rich mixture, boiling point 174-l75 C. at 1.3-1.1 -mm.,collected. This mixture was subjected to alkaline hydrolysis to for-mthe sodium salt which was sprung with HCl. The resulting acidic mixturecontained 17.1% of monochloro-methylbenzoic acid, 3.6% 72.1% of oneisomer of dichloro-methylbenzoic acid, and 7.2% of a second isomer ofdichloromethylbenzoic. After recrystallization from octane a relativelypure product was obtained. This recrystallized pnoductcontained 9.4% ofmethylchlorobenzoic acid, 3.25% of methyltrichlorobenzoic acid, 83.85%of 3,5-dichloro-2-methylbenzoic acid, and 3.5% of a material which waseither 3,4-dichloro- Z-methylbenzoic acid or4,5-dichloro-Z-methylbeuzoic acid, or a mixture of these isomers.

Fraction B containing the di-ortho substituted acids was refluxed withSOCl to form the corresponding benzoyl chlorides. The chlorides weredistilled and a fraction, boiling point 104-107 C. at 1.4-1.8 mm, wasseparated, hydrolyzed with aqueous sodium hydroxide, and converted tothe acid with HCl. It was established that this product was 99.9% pure2,3-dichloro-6-methylbenzoic acid.

Example 8 TABLE V.PRE-EMERGENCE INJURY RATING C'ompound IAbsJ C0 01 Wh0t On Sb Rg Mu Mg Bw Cg Y! cre 2,3-dichloro-6-methyl- 0.5 0 10- 10 10 1010 0 10 10 10 0 0 2.0 10 10 10 10 10 10 10 10 0 10 '0 02-n1ethyl-3,5-dichlor0 0.5 0 0 0 0 0 0 '0 10 0 O 0 0 2.0 0 0 0 0 0 10 00 10 0 0 0 2,3-Dichl0ro 0.5 0 0 0 0 0 s 0 10 0 0 0 2.0 0 0 0 0 10 s 0 s0 0 0 0 2,44) 0.5 0 510 0 s 8 01010 0 0 0 2.0 0 s 10 10 10 ,10 5 10 10 00 0 4.0 10 10 10 10 10 10 0 10 10 s 10 10 of trichloro-methylbenzoicacid,.

TABLE VI.-POST-EMERGENCE INJURY RATING Compound libs] C 01 W11 0t On ShRg Mu Mg Bw Cg Yf cre 2,3-dicholro-6-methyl 0. 0 0 0 10 10 0 10 8 5 0 02. 0 0 10 0 0 10 10 0 10 10 10 0 0 2-n1ethyl-3,5-dichloro 0. 5 0 0 0 0 00 0 0 0 0 0 0 2.0 0 0 0 0 0 1 0 l0 4 0 0 0 2,3-dichloro 0. 5 0 0 0 0 5 00 8 0 0 0 0 2. 0 0 0 0 0 5 10 0 10 0 0 0 0 2,4-D- 0. 5 0 0 O 0 8 8 0 1010 9 0 0 2. 0 0 10 0 0 10 10 0 10 10 10 0 0 4. 0 0 l0 0 0 10 10 0 10 109 2 O 2,3-Dichloro-6-methyl=salt of ZS-dichJoroS-methylbenzoic acid.2-Methyl-3,5-dichloro=salt of 2-methy1 3,&dich1orobenzoic acid.2,3Dicl1l0ro=sa1t of 2,3-dichlorohenzoic acid. 2,4 D=salt of2,4-dichlorophenoxyacetie acid.

Co=Corn. Rg= Ryegrass.

Cl= Clover. Mu=Mustard.

Wh=Wheat. Mg=lWIorning glory.

OT= Oats. Bw=Buckwheat.

On= Onions. Og= Crabgrass.

Sb=Soybeans. Yf= Yellow i'oxtail. Injury Rating.-

0=No visible effect.

1, 2, 3=Indicates slight injury; plant usually recovered with little orno reduction in top gro 4, 5, 6=Moderate injury; plant usuallyrecovered, but with reduced top growth.

7, 8, 9=Severe injury; plants did not recover.

10=All plants killed.

In the post-emergent tests the clover and onions were planted 19 daysbefore treatment; the mustard, crabgrass and yellow foxtail were planted16 days before application of the herbicide; the corn, soybeans, morningglory and buckwheat were planted 12 days before treatment; and thewheat, oats, and ryegrass were planted 9 days before treatment of theflats with the compounds being tested. All observations were made 14days after treatment.

While 2,3dicb1oro-6-methylbenzoic acid and Z-methyl- 3,6-dichlorobenzoicacid have been discussed in greater detail, h-omolog'ues of these twoacids are effective herbicides for the same purpose. The2,3-dichloro-6-alkylbenzoic acids and 2-alkyl-3, 6-dichlorobenzoic acidsmay be prepared in any suitablemanner. For example, 2-propyl-3,6-dichlorobenzoic acid can be prepared fromortho-bromo-toluene. When this material is nuclear dichl-orinated, oneof the isomers formed is 2-bromo-3,6- dichlorotoluene. The methyl groupcan be converted to a carboxyl group by oxidation with nitrous oxide andair. By the Fittig reaction utilizing propyl bromide in the presence ofsodium metal, the bromine of the 2-brom0-3,6- dichlorobenzoic acid isreplaced with a propyl group to form 2 propyl-3,6dichlorobenzoic acid.By using methyl, ethyl or butyl bromide in place of propyl bromide, thecorresponding methyl, ethyl or butyl compounds may be formed.

Propyl benzene can be monobr'ominated to form a mixture of oand p-bromopropyl benzene. These isomers can be separated by distillation. Nucleardichlorination of the ortho bromo compound will produce a mixture of2-bromo-3,4-dichloro and 2-bromo-3,6-dichloro propyl benzene. By theGrignard reaction utilizing magnesium followed by treatment with CO gasin the presence of water, the bromine atoms are replaced with ear-boxylgroups. The resulting reaction mixture contains Z-propyl-3,6-dichlorobenzoic acid and 2,3-dichloro-6-propyl benzoic acid. Theseacids may be separated, if desired, or used .as such as herbicides. Bystarting with toluene, ethyl benzene or butyl benzene, the correspondingdichloro-monoalkyl benzoic acids can be formed.

We claim:

1. A compound selected from the group consisting ofmonoalkyldichlorobenzoic acids having the formula:

COOH

wherein one of the symbols R and R is a chlorine atom and the other isan alkyl group containing from 1 to 4 carbon atoms; the alkali metalsalts of such acids, the alkaline earth metal salts of such acids, theammonium salts of such acids, the monoand dialkylamine salts of suchacids in which the alkyl groups contain from 1 to 4 carbon atoms, andthe monoand dialkanolamine salts of said acids; and mixtures thereof.

2. An alkali metal salt of 2,3-dichloro-6-methylbenzoic acid.

3. An alkali metal salt of 2- methyl-3,6 dichlorobenzoic acid.

4. 2,3-dichloro-6-methylbenzoic acid.

5. 2-methyl-3,6-dichlorobenzoic acid. 6. The sodium salt of2,3-dichloro-6-methylbenzoic acid.

References Cited by the Examiner UNITED STATES PATENTS 1,858,625 5/1932Hofia 260515 2,394,916 5/ 1945 Jones 7l2.6 2,848,470 8/1958 Girard et al260-515 2,992,913 7/ 1961 Pfeiflfer 260-515 OTHER REFERENCES ChemicalAbstracts, Vol. 22, subject index, p. 6387,

Cohen et al., J. Chem. Soc, vol. 79, p. 1128 (1901).

LORRAINE A. WEINBERGER, Primary Examiner.

R. E. MASSA, T. L. GALLOWAY, Assistant Examiners.

1. A COMPOUND SELECTED FROM THE GROUP CONSISTING OFMONOALKYLDICHLOROBENZOIC ACIDS HAVING THE FORMULA:1-(HOOC-),2-R1,3-CL,6-R-BENZENE WHEREIN ONE OF THE SYMBOLS R AND R'' ISA CHLORINE ATOM AND THE OTHER IS AN ALKYL GROUP CONTAINING FROM 1 TO 4CARBON ATOMS; THE ALKALI METAL SALTS OF SUCH ACIDS, THE ALKALINE EARTHMETAL SALTS OF SUCH ACIDS, THE AMMONIUM SALTS OF SUCH ACIDS, THE MONO-AND DIALKYLAMINE SALTS OF SUCH ACIDS IN WHICH THE ALKYL GROUPS CONTAINFROM 1 TO 4 CARBON ATOMS, AND THE MONO- AND DIALKANOLAMINE SALTS OF SAIDACIDS; AND MIXTURES THEREOF.